AGRONOMIC EFFICIENCY AND ECONOMIC RETURNS OF UPLAND RICE AS INFLUENCED BY FERTILIZER APPLICATION AND CULTIVARS IN UYO, SOUTHEASTERN NIGERIA ABSTRACT Aderi, O. S. and Ndaeyo, N. U. Department of Crop Science, University of Uyo, Uyo, Nigeria, Email: ofsamaus@yahoo.com Field experiments were conducted at the Teaching and Research Farm of the Faculty of Agriculture, University of Uyo to assess the effects of combined application of organic (poultry manure PM) and inorganic fertilizer (NPK- 15-15-15 ) and cultivars on the agronomic efficiency (AE) and economic returns (ER) on upland rice production. A 6 x 5 factorial arrangement laid out in a randomized complete block design with three replicates was used. Six fertilizer combinations: 6.0 tha -1 PM sole, 400 kg ha -1 NPK sole, 4.5 t ha -1 PM + 100 kg ha -1 NPK, 3.0tha -1 PM + 200 kg ha -1 NPK, 1.5 tha -1 PM + 300 kg ha -1 NPK, and a control and five upland rice cultivars; 43, 46, 55, 56 and a local check (- Otokongtian) were the treatments. Results showed that in both years the highest significant AE was obtained from 3.0 t ha -1 PM + 200 kg ha -1 NPK treatment (51.57 and 54.72 kg per kg for 2009 and 2010 respectively), followed by 1.5 tha -1 PM + 300 kg ha -1 NPK (47.69 and 48.33 kg per kg for 2009 and 2010 respectively). The lowest AE was obtained from 6.0 t ha -1 PM sole (39.42 and 38.02 respectively for 2009 and 2010). In both years, 43 produced the highest significant (p= 0.05) AE, followed by 56. The interaction effects indicated that cultivars generally, produced significantly higher AE with the application of 3.0 t ha -1 PM + 200 kg ha -1 NPK. There was significant correlation between AE and grain yield for both years r = 0.99. The highest economic return on investment due to fertilizer combination (means across cultivars) was obtained from 3.0 t ha -1 organic + 200 kg ha -1 NPK combination and gave 217% and 237% net return in 2009 and 2010, respectively compared to the control. The highest economic returns due to cultivar effects (means across fertilizer combinations) was obtained from 43 in 2009 (222.5%) and 2010 (220.8%). Therefore, it is obvious that combined application of PM (3.0 tha -1 ) and NPK (200 kgha -1 ) fertilizer with 43 will increase the AE and ER of upland rice relative to using mononutrient source. Keywords: Agronomic efficiency, upland rice, fertilizer, economic return. INTRODUCTION Nigeria has one of the lowest mineral fertilizer consumption rates in the world (FOASTAT FERTILIZER, 2015). Nigeria s fertilizer nitrogen consumption is about ¼ th of South Africa s rate, 1 / 10 th of Egypt s rate and 1 / 14 th of Thailand s. The low rate of fertilizer consumption is caused by such factors as government policy on fertilizer deregulation, high cost, inadequate availability to farmers, poor distribution network, high transport cost and, more importantly, low yield response to inorganic fertilizer application (Saweda et al., 2015). Fortunately, the country is endowed with different organic waste sources such as poultry manure, oil palm bunch, farmyard manure, compost manure, cocoa pod husk, fluted pumpkin pod husks, kola pod husks, cowpea husk, plantain/banana peels, citrus fruit waste, and other biodegradable organic wastes, treated water treatment sludge, and composted materials which have been reported to improve the nutrient status of soils and hence crop yield. The major source of organic waste used in agriculture is animal manure (Westerman and Bicudo, 2005). In Nigeria, animal manure is produced principally by cattle, pig, goat, sheep and poultry. It is estimated that Nigeria produced 16.29 million cattle, 6.91million pigs, 53.80 million goats, 33.87 million sheep, and 175 million chicken in 2008 (Arthur and Baidoo, 2011). Ngumah et al. (2013) reported that organic wastes generated annually by livestock and other sources in Nigeria are as follow: cattle manure, 197.6, sheep and goat manure, 39.6, pig manure, 15.3, poultry manure, 32.6, human manure, 52.0, crop residues, 83.0, abattoir waste, 83.3, municipal solid waste, 39.1, with a total of 542.5 million tons annually. Ojeniyi (2012) noted that organic wastes were found to be effective in increasing soil nutrient contents, ph and nutrient uptake by crops, soil organic matter, and when combined with inorganic fertilizer for application in crop production, had a synergistic effect on each other. Applications of organo-mineral fertilizer have been reported to have given similar or higher crop yield compared to recommended NPK fertilizer rate, improved nutritional quality and nutrient content of crops and had residual effect than inorganic fertilizer (Ojeniyi, 2012). Therefore, for sustainable productivity of the land resource to meet the increasing population and for high returns on investment, especially for cereal production system that provides more than 60% of human dietary calories (Cassman et al., 2002), there is need to increase the productivity of the available land through adoption of proper soil nutrient management and protection. In rice nutrition, nitrogen application is reported to have improved grain yield (Walker et al., 2006). Nitrogen use efficiency in rice is however, influenced by a number of factors-environmental and crop. Nielsen (2006) defined nitrogen use efficiency (NUE) as a measure of crop production per unit of nitrogen input. Fageria et al. (2010) NJAFE VOL. 12 No. 2, 2016 119
classified NUE of rice into agronomic efficiency (AE), apparent recovery efficiency (ARE), and utilization efficiency (EU). They defined AE as the economic production (grain yield) obtained per unit of nitrogen applied. Mae et al. (2006) reported that AE varied with cultivars and tended to decrease with increased N application due to reported synergy between organic and inorganic fertilizer combination. Therefore, the objective of this study was to evaluate the effects of organic and inorganic fertilizers on the agronomic efficiency and economic returns on the production of some upland rice cultivars. MATERIALS AND METHODS Field experiments were conducted during the cropping seasons of 2009 and 2010 at the Teaching and Research Farm of the Faculty of Agriculture, University of Uyo, located at Use Offot, Uyo, Akwa Ibom State. The experimental plots were located between latitudes 05 01 56.2 and 05 01 56.6 N and longitudes 07 58 20.2 and 07 58 20.6 E and 55-57 m above sea level. Peters (1989) reported that the area is in the humid rain forest zone, receives an annual rainfall of about 2,500 mm with a mean relative humidity of 87%. The mean annual temperature varies between 22 and 32 C with sunshine hours of 3-8. The soil is acidic and belongs to the broad soil classification group, ultisol. Rice seeds were were sown on May 12, 2009 and May 22, 2010. The land was planted with cassava in 2006 and harvested in 2007 with a fallow period of one year (2008). Experimental design and treatments A 6 x 5 factorial arrangement laid out in a randomized complete block design with three replicates was used. Treatments were six fertilizers (6.0 t ha -1 PM sole, 400 kg ha -1 NPK sole, 4.5 t ha -1 PM + 100 kg ha -1 NPK and a control and five upland rice cultivars ( 43, 46, 55, 56 and a local check (Otokongtian) were the treatments. Poultry manure was applied to the required plots by uniform broadcasting and then worked into the soil with spade. Sample of poultry manure was obtained for analysis in the Soil Science Laboratory for total nitrogen by the kjeldahl procedures described by Udo and Ogunwale (1986). Cultural Practices Rice seeds obtained from National Cereals Research Institute, Badeggi were sown two weeks after the application of PM by dibbling method at 25cm x 25cm spacing. Six seeds were sown per hill and thinned down to four seedlings per hill at two weeks after sowing. NPK fertilizer was applied in three equal one third split doses at sowing, mid tillering stage and panicle initiation stage (Fageria, 2010). All the plots were maintained weed free with pre-emergent herbicide (paraquat at 1.0 kg active ingredient per hectare) followed by two hand weeding at 3, 6, 9 and 12 weeks after sowing. Data collection Grain yield was estimated by the method described by Fageria (1992) as follow: Grain yield (t ha -1 ) = number of panicles m -2 x number of spikelets per panicle x percentage of filled spikelets x average grain weight of 1,000 grains x 10-5. Agronomic efficiency was obtained by the formula of Fagaria et al. (2010) as: AE = Gf Gu Na Where, AE = Agronomic efficiency Gf = the grain yield of the fertilized plot Gu = the grain yield of the unfertilized plot Na = quantity of nitrogen applied Data on AE were analyzed using Genstat Discovery Edition. Analysis of economic returns on investment was done using crop enterprise budget techniques (Wesley et al., 1993) expressed as follow: Extra benefit from the new technology x 100 Extra investment in that new technology 1 RESULTS Apart from the control (without fertilizer application), the total N applied from 6.0 tha -1 PM sole was significantly higher than N applied from 400 kg ha -1 NPK sole, 1.5 t ha -1 PM + 300 kgha -1 NPK, and 3.0 t ha -1 PM + 200 kg ha - 1 NPK in both years (Table 1). The content of N in 6.0 t ha -1 PM sole was similar to N in 4.5 t ha -1 PM + 100 kg ha -1 NPK combination while 400 kg ha -1 NPK sole was similar in N to 1.5 t ha -1 PM + 300 kg ha -1 NPK. Similarly, 3.0 t ha -1 PM + 100 kg ha -1 NPK contained similar N with 1.5 t ha -1 PM + 300 kg ha -1 NPK in both years. The 3.0 t ha -1 PM + 200 kg ha -1 NPK produced the highest significant agronomic efficiency (51.57 kg kg -1 ) in 2009 followed by 1.5 t ha -1 PM + 300 kg ha -1 NPK (Table 2). The 6.0 t ha -1 PM sole produced the lowest AE (39.42 kg kg -1 ). The 43 cultivar produced the highest significant AE (52.37 kg kg -1 ), followed by 56. The lowest AE (18.43 kg kg -1 ) was obtained from 46. The interaction effect between fertilizers and rice cultivars showed that cultivars in general produced higher AE on application of 3.0 t ha -1 PM + 200 kg ha -1 NPK. In 2010, 3.0 t ha -1 PM + 200 kg ha -1 NPK also produced the highest AE followed by 1.5 t ha -1 PM + 300 kg ha -1 NJAFE VOL. 12 No. 2, 2016 120
NPK. The 6.0 t ha -1 PM sole consistently produced the lowest AE. The effects of rice cultivars and the interaction followed similar trend observed in 2009. There was a significant positive correlation between agronomic efficiency and grain yield in both years (Table 3). It indicated that the higher the agronomic efficiency, the higher the grain yields. The highest marginal rate of returns (means across cultivars) was obtained from 3.0 t ha -1 PM + 200 kg ha -1 NPK and it represented 237% and 217% returns on investment in 2009 and 2010, respectively compared to the control (Table 4). It was followed by 6.0 t ha -1 PM sole which gave a net positive return on investment in 2009 (marginal revenue of 288.7% over the control), but a net negative return (259.4%) in 2010. Cultivar effect (means across fertilizer combinations) indicated marginal rate of return for 43 to be the highest in both years (222.5% and 220.8% for 2009 and 2010, respectively) compared to the check (Table 5). Other rice cultivars did not give higher net benefits than the local check (Otokongtian). DISCUSSION The study showed synergistic effect of combined application of poultry manure and NPK fertilizer for the production of upland rice. Although the total nitrogen contents of 6.0 tha -1 PM sole and 4.5 t ha -1 PM + 100 kg ha - 1 NPK were the highest, these did not translate into higher agronomic efficiencies in comparison with 3.0 tha -1 PM + 200 kg ha -1 NPK and 1.5 t ha -1 PM + 300 kg ha -1 NPK combinations. The high carbon: nitrogen ratio of the poultry manure used (21.5:1 in 2009 and 31: 1 in 2010) might have immobilized some N in PM. Application of poultry manure at a rate as low as 1.5 t ha -1 in combination with 300 kg ha -1 NPK increased the AE significantly over 6.0 t ha -1 PM applied sole. Application of 3.0 t ha -1 PM + 200 kg ha -1 NPK increased AE more than the values for both PM and NPK sole. This finding agrees with the report of Ojeniyi (2012) that combined application of organic waste with inorganic fertilizer had a synergistic effect on each other by increasing soil nutrient contents, moderating soil ph, improving nutrient uptake by crops and soil organic matter. Tirol-Padre et al. (2007) reported increased mineralization of N and availability for uptake by plants in the soil due to combined application of organic manure and inorganic fertilizer. Nitrogen deficiency is related to N losses in various forms leaching, volatilization denitrification and runoff losses (Fageria and Baligar, 2005), and it appeared that increased soil organic matter due to application of organic manure minimized N losses in addition to other synergistic effects. Agronomic efficiency differed with rice cultivars. Fageria (2007) noted that upland rice genotypes differed significantly in nitrogen uptake and utilization efficiency. The use of N-efficient genotypes in combination with appropriate fertilizer application is an important complementary strategy in improving rice yield and reducing cost of production. The highest AE was obtained from 43, followed by Otokongtian in both years. These two cultivars showed efficient N use by their high grain yield. According to Mac et al. (2006) AE varied with cultivars and tended to decrease with increased N rate. Fageria et al. (2010) reported significant differences among 19 upland rice genotypes in their agronomic efficiency and utilization that varied from 12.8 to 26.7 mg grain per mg N applied with an average value of 21.4 mg mg -1. The highest grain yield producing genotype- 43 had the highest AE (26.7 mg grain per mg N), whereas the lowest yielding genotype- 46 had the lowest AE 12.8 mg mg -1 ). Genotypic differences could be accounted for, in part, by N volatilization from plant tissues and death of partial leaf and organ at post flowering stage. In this study, N volatilization from 43 and 56 could have been highly minimized as a result of the genetic constitution that apparently gave them advantage over other cultivars. More revenue was realized from applying 3.0 t ha -1 PM + 200 kg ha -1 NPK in both years. However, cost of production increased further in the succeeding year mostly due to high cost of mineral fertilizer, labour for application, transportation and weeding. The cultivation of 43 consistently gave higher net benefit and return on investment compared to other cultivars. CONCLUSION Based on the research findings it is concluded that agronomic efficiency and economic return on investment of upland rice increased with combined application of poultry manure and mineral (NPK 15-15-15) fertilizer mostly at 3.0 t ha -1 PM + 200 kg ha -1 NPK. The 43 cultivar produced the highest agronomic efficiency and net return on investment. Proper combination of organic and inorganic fertilizer and varietal selection can improve the agronomic efficiency and economic returns on upland rice production. NJAFE VOL. 12 No. 2, 2016 121
Table 1: Effects of fertilizer combinations on estimated total nitrogen application Fertilizer Combination Quantity of poultry Estimated quantity N Total N (kg ha -1 ) manure (kg) estimated from PM + NPK (t ha -1 ) 2009 2010 2009 2010 Control 0.00 0.00 0.000 0.00 0.00 1.5 tha -1 PM + 300 kgha -1 NPK 1.50 16.65 16.73 61.65 61.73 3.0 tha -1 PM + 200 kgha -1 NPK 3.00 33.30 33.45 63.30 63.45 4.5 tha -1 PM + 100 kgha -1 NPK 4.50 49.95 50.18 64.95 65.18 6.0 tha -1 PM sole 6.00 66.60 66.90 66.60 66.90 400 kgha -1 NPK sole (0.00) (60.00) (60.00) 60.00 60.00 Mean 52.8 52.9 Standard Error 2.1 2.2 Standard Deviation 5.2 5.4 Coefficient of Variation 9.8 10.2 Table 2: Effects of poultry manure and NPK fertilizer combinations on the agronomic efficiency (kg kg -1 ) of rice in 2009 and 2010 in Uyo Nigeria Fertilizer Combinations 43 46 55 56 Otokongtian 2009 Control - - - - - - 1.5 t ha -1 PM + 300 kg ha -1 NPK 64.22 22.97 46.35 57.65 47.27 47.69 3.0 t ha -1 PM + 200 kg ha -1 NPK 74.75 23.87 49.65 56.73 52.85 51.57 4.5 t ha -1 PM + 100 kg ha -1 NPK 62.03 20.82 43.16 49.44 46.27 44.34 6.0 t ha -1 PM sole 54.18 19.01 40.67 46.99 36.24 39.42 400 kg ha -1 NPK sole 59.06 23.89 46.72 49.33 49.06 45.61 Mean 62.85 22.11 45.31 52.03 46.34 45.73 2010 1.5 t ha -1 PM + 300 kg ha -1 NPK 71.91 25.65 38.93 57.94 47.23 48.33 3.0 t ha -1 PM + 200 kg ha -1 NPK 76.43 31.42 48.37 63.51 53.86 54.72 4.5 t ha -1 PM + 100 kg ha -1 NPK 66.72 22.87 35.80 52.73 44.89 44.60 6.0 t ha -1 PM sole 53.91 23.86 35.89 39.23 37.20 38.02 400 kg ha -1 NPK sole 54.44 24.83 39.39 44.56 48.33 42.31 Mean 64.68 25.73 39.68 51.59 46.30 45.60 2009 2010 LSD (=.05) for fertilizer combination means (F) 3.50 1.93 LSD (=.05) for cultivars means (C) 3.19 1.76 LSD (=.05) for F x C means 7.82 4.32 Table 3: Correlation coefficient (r) between agronomic efficiency and grain yield of upland rice Year Correlation Coefficient (r) 2009 0.99* 2010 0.99* * Significant at 5% level of probability. Mean NJAFE VOL. 12 No. 2, 2016 122
Nigerian Journal of Agriculture, Food and Environment. 12(2):119-118 Table 4: Cost of production of upland rice as influenced by combined application of PM and NPK fertilizers (means across cultivars) in 2009 and 2010 in Uyo, Nigeria 6.0 t/ha PM 400 kg ha -1 NPK 4.5 t ha -1 PM + 100 1.5 t ha -1 PM + 300 3.0 t ha -1 PM + 200 Control Operation kg ha -1 NPK kg ha -1 NPK kg ha -1 NPK 2009 2010 2009 2010 2009 2010 2009 2010 2009 2010 2009 2010 Average crop yield (t ha -1 ) 3.68 3.89 3.84 3.80 3.94 4.24 4.03 4.27 4.34 4.80 1.10 1.27 Gross revenue (Nha -1 ) 432,440 458,480 453,000 449.320 464.520 499.800 474.600 503.600 510.950 564.520 130.800 148.600 Pre-sowing Soil Analysis 2,500 2,500 2,500 2,500 2,500 2,500 2,500 2,500 2,500 2,500 2,500 2,500 Land preparation and marking 35,000 43,000 35,000 43,000 35,000 43,000 35,000 43,000 35,000 43,000 35,000 43,000 Labour 259,037 347,724 294,121 385,517 308,734 411,400 307,714 411,737 310,902 417,233 220,041 298,269 Seed purchases 6,860 6,860 6,860 6,860 6,860 6,860 6,860 6,860 6,860 6,860 6,860 6,860 Organic fertilizer (chicken manure) purchase and transport of 56,000 58,000 0.00 0.00 42,000 43,500 15,500 16,000 28,000 28,000 0.00 0.00 Inorganic fertilizer (NPK 15:15:15) 0.00 0.00 64,000 64,800 16,000 16,200 48,000 48,600 32,000 32,500 0.00 0.00 Insecticide purchase 4,400 4,400 4,400 4,400 4,400 4,400 4,400 4,400 4,400 4,400 4,400 4,400 Herbicide purchase 9,500 12,000 0.00 0.00 9,500 12,000 9,500 12,000 9,500 12,000 9,500 12,000 Total Cost (N) 373,297 474,484 406,881 507,077 422,994 539,860 429,474 545,097 429,162 546,893 268,801 366,029 Net Benefit (N) 59,143-16,004 46,119-57,757 41,526-40,060 45,126-41,497 81,788 17,627-138,001-206,429 Marginal Rate of Return (%) 288.66 259.41 233.34 194.78 216.43 190.01 213.97 186.78 237.06 216.78 - - Cost/Benefit Ratio 1.16 0.97 1.11 0.89 1.10 0.93 1.11 0.92 1.19 1.03 0.49 0.42 NJAFE VOL. 12 No. 2, 2016 123
Nigerian Journal of Agriculture, Food and Environment. 12(2):119-118 Table 5: Cost of production and Economic returns of upland rice as influenced by cultivars (means across poultry manure and NPK fertilizer combinations) in 2009 and 2010 in Uyo, Nigeria 43 46 55 56 Otokongtian Operation 2009 2010 2009 2010 2009 2010 2009 2010 2009 2010 Average crop yield (t ha -1 ) 4.54 4.83 2.25 2.38 3.38 3.50 3.73 4.06 3.54 3.80 Gross revenue (Nha -1 ) due 547,200 582,300 271,500 286,500 362,133 374,400 399,733 435,467 474,667 508,333 cultivars Cost of (N): Seed purchase 7,280 7,280 8,760 8,760 7,880 7,880 7,040 7,040 3,340 3,340 Seed sowing 16,000 16,000 16,000 16,000 16,000 16,000 16,000 16,000 16,000 16,000 Panicle harvesting 28,370 30,160 14,090 14,860 21,120 21,850 23,300 25,390 22,150 23,720 Threshing 19,156 20,380 9,494 10,042 14,262 14,768 15,738 17,131 14,937 16,034 Parboiling 34,068 36,244 16,884 17,860 25,364 26,264 27,990 30,466 26,564 28,515 Milling 48,640 51,680 24,160 25,440 36,160 37,440 40,000 43,520 37,920 40,640 Total cost (Nha -1 ) Due to 153,514 161,744 89,388 92,962 120,786 124,202 130,068 139,547 120,900 128,249 cultivars Net benefit (N) 393,686 420,556 182,112 193,538 241,347 250,198 269,665 295,920 353,756 380,084 Marginal rate of return (%) 222.5 220.8-644.5-628.7-90027.2-3309.4-818.3-644.9 - - Cost:benefit ratio 3.56 3.60 3.04 3.08 3.00 3.01 3.07 3.12 3.93 3.96 REFERENCES Arthur, R. and Baidoo, M. F. 2011. Harnessing methane generated from livestock manure in Ghana, Nigeria.. Mali and Burkina Faso. Biomass and Bioenergy, 35:4648-4656. Cassman, K. G., Dobermann, A. and Walkers, D. T. 2002. Agroecosystems, nitrogen-use efficiency, and nitrogen management. Ambio, 31(2):132-140. Fageria, N. K. 1992. Maximizing crop yields. Marcel Dekkar, Inc. New York. p65. Fageria, N. K. 2007. Yield physiology of rice. Journal of Plant Nutrition, 30:843-879. Fageria, N. K. 2010. Optimal nitrogen fertilization timing for upland rice. 2010 19 th World Congress of Soil Science, Soil Solutions for a Changing World. 1 6 August 2010, Brisbane, Australia. pp. 1-4. NKF Optimalz+v12F.pdf. 2013 Fageria, N. K. and Baligar, V. C. 2005. Enhancing nitrogen use efficiency in crop production. Advances in Agronomy, 88:97-105. Fageria, N. K., de Morais, O. P. and dos Santos, A. B. 2010. Nitrogen use efficiency in upland rice Genotypes. Journal of Plant Nutrition, 33:1696-1711. FAOSTAT Fertilizer (Food and Agriculture Organization) Statistical Database-Fertilizer. 2015. Mineral Fertilizer Consumption. Mae, T., Inaba, A., Kaneta, Y., Masaki, S., Sasaki, M., Aizawa, M., Okawa, S., Hasegawa, S. and Makino, A. 2006. A large-grain rice cultivar, Akita 63, exhibits high yields with high physiological N-use efficiency. Field Crops Research, 97(2-3): 227-237. Ngumah, C., Ogbulie, J., Orji, J. and Amadi, E. (2013). Potential of organic waste for biogas and biofertilizer production in Nigeria. Environmental Research, Engineering and Management, 1(63):60-66. Nielsen, R. 2006. N loss mechanisms and nitrogen use efficiency. Purdue Nitrogen Management Workshops: Purdue University, West Lafayette, Indiana, U S A. pp. 1-5. Ojeniyi, S. O. 2012. Advances in integrated nutrient management for crop production in Nigeria. Nigerian Journal of Technological Research, 7(3), Special Edition. Saweda, L. T., Bolarin, T. O., Awa, S. and Wale, O. 2015. Inorganic fertilizer use in Africa: Not too low but not too profitable Evidence from Nigeria. Agriculture in Africa: Telling Facts from Myths. Peters, S. W. 1989. Physical background, soils, land use and ecological problems. Technical Report of the Taskforce on Soils and Land Use Survey, Akwa Ibom State. The Government Printer, Uyo. Tirol-Padre, A., Ladha, J. K., Regma, A. P., Bhandar, A. L. and Incibushi, K. 2007. Organic amendments affect soil parameters in two long-term rice-wheat experiments. Soil Science Society of American Journal, 71:442-452. Udo, E. J. and Ogunwale, J. A. 1986. Laboratory manual for the analysis of soil, plant and water samples. Ibadan: Department of Agronomy, University of Ibadan. Walker, J. W., Martin, S, W. and Gerard, P. D. 2006. Grain yield and milling quality response of two rice cultivars to top-dress nitrogen application timing. Agronomy Journal, 98:1495-1500. Wesley, R. A. Smith, L. A. and Spurlock, S. R. 1993. Economic analysis of irrigation and deep tillage in soybean production systems on clay soil. Soil and Tillage Research, 28:63-78. Westerman, P. W. and Bicudo, J. R. 2005. Management considerations for organic waste in agriculture. Bioresource Technology, 96(2):215-221. NJAFE VOL. 12 No. 2, 2016 124